Field of the Invention
The present invention relates to an image processing apparatus and a method of controlling an image processing apparatus.
Description of the Related Art
Generally, in an image capturing apparatus such as a digital camera, shaking of the actual image capturing apparatus is detected, and image blur caused by this camera shake is corrected. When this correction is performed, a movable lens member (an image stabilization lens and a holding member for the same) that can be shifted is driven by an image stabilization apparatus so as to correct the image blur.
Also, there are many cases in which an angular velocity meter and an accelerometer are used when detecting camera shake in the image stabilization apparatus. For example, an image stabilization device that detects angular shake using an angular velocity meter and suppresses image blur by moving a portion of imaging lenses or an image sensor is built into various optical instruments. However, in close range shooting, it is not possible to ignore image degradation caused by vibration that cannot be detected by the angular velocity meter alone, in other words so-called translational shake acting in the horizontal direction or the vertical direction in a plane orthogonal to the optical axis of the camera. For example, in the case of macro imaging in which the camera is approximately 20 cm away from a subject, there is a need to proactively detect and correct the translational shake. An accelerometer is often used to detect this translational shake.
The image stabilization apparatus obtains a camera shake amount and direction from obtained angular velocity information and acceleration information, and outputs a correction position control signal for driving the movable lens member so as to cancel out the image blur. When the movable lens member is driven, the current position of the movable lens member is fed back to the image stabilization apparatus as a movable member position signal. Then, the image stabilization apparatus performs feedback control to output a correction position control signal that corresponds to the movable member position signal.
Also, an image stabilization device and an image capturing apparatus have been proposed with which power saving can be achieved by activating and stopping image stabilization in accordance with the focal length and the distance to a subject (imaging magnification) when a subject image is displayed as a moving image on an LCD (see Japanese Patent Laid-Open No. 2013-104921). With a digital camera, a moving image can be displayed on the screen of an LCD or the like, but there are cases in which even if camera shake influences the recorded subject image, it will not influence the subject image displayed as a moving image, that is to say the user will not perceive the image blur. In the case in which image stabilization is also executed during moving image display, image stabilization is executed even if the camera shake has no influence on the moving image during wide angle shooting, and thus power is wastefully consumed.
In view of this, in Japanese Patent Laid-Open No. 2013-104921, control such as the following is proposed for the period in which a moving image sensed on a wide angle side with a short focal length is being displayed. Specifically, it is determined whether or not the displacement amount of the subject image for display due to camera shake exceeds the pixel pitch of the display screen, and in the case in which the user cannot perceive image blur in the subject image for display, or in the case in which the user is not bothered by the image blur very much, either the degree of stabilization operation of the image stabilization mechanism is reduced or an operation stop state is entered. On the other hand, in the case in which the user can perceive image blur of the subject image for display, the image stabilization mechanism is activated, and the degree of stabilization operation is increased. Also, as explained before, when the subject is at a close range and the magnification ratio is high as in macro imaging, the influence of the angular shake and the translational shake increases, and thus even in wide angle shooting, the image stabilization mechanism is made active in accordance with the distance to the subject in order to raise the suppression effect.
Also, in image data obtained by an image capturing apparatus, there is generally a tendency for the margins, including the four corners, to be darker than the center. Particularly, the phenomenon in which the amount of light in the margins decreases relative to the center is called “shading”. The larger the decreasing rate of the amount of light in the margin portion relative to the center (marginal illumination) is, the worse the image data quality becomes. A decrease in the marginal illumination is an intrinsic characteristic of the lenses, and for this reason it can be said to be the characteristic that causes variance in the luminance in the four corners. The decreasing rate of the marginal illumination changes in accordance with the zoom magnification rate, that is to say the zoom lens position as well. Furthermore, when the image stabilization lens shifts from the optical axis, the amount of light in the region on the side opposite to the shifted direction decreases, and attachment position error of the image sensor and the like is also a factor in the decrease in the amount of light. There has been a need to determine a movable range for a correction lens so that shading does not have an influence on images to be displayed or recorded, taking into consideration all of these factors in the decrease in the amount of light.
Furthermore, depending on the arrangement of an optical lens group, there are cases in which the amount of light also decreases due to the position of the focus lens that performs focus adjustment. For example, if the mechanism of the focus lens group is an inner focus type, there are cases in which the effective focal length decreases due to shifting the position of the focus lens to the front lens side for the purpose of being in focus when performing macro-imaging at close range, and thus the marginal illumination decreases.
For this reason, in the case of determining the movable range of the correction lens at each zoom lens position as described in Japanese Patent Laid-Open No. 2013-104921, there has been an issue in which a decrease in marginal illumination becomes noticeable when performing macro imaging, depending on the arrangement of the optical lens group. Also, if the movable range is set according to the movable range when performing macro-imaging, there has been an issue in which the movable range in a normal shooting range becomes narrow, and a sufficient correction effect cannot be obtained for large camera shakes such as those that occur when shooting while walking.